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VLC media player supports many audio and video compression methods and file formats, including DVD-video, video CD and streaming protocols. It is able to stream over computer network and to transcode multimedia files. (from Wikipedia)

Tested many media players before and still stuck on Winamp with no real solution for Ubuntu. Clementine import my music awesomely fast compared to amarok. Neat GUI. Important feature configurable (like behavior when double click on album). Powerful tag edition embedded. I am a fan. Thank you. you made my day
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UgoMay 13 '11 at 22:32

MPlayer is also a good one, which makes a good choice for scripting, since it provides feedback when exiting (e.g. Exiting... (End of file)), and allows you to react upon this, e.g. mark the file as played.

It's available in Ubuntu, in different flavors (e.g. mplayer-gui or just mplayer).

Recent versions (now 0.6.2) bring it even closer to the purpose of becoming a Foobar2000 alternative by the 'Designer mode' feature that lets you add or remove features. The main addons like the File browser and Infobar (lyrics and biography) can be added in this way.

This media player supports the vlc, xine and GStreamer engines for playing media. Since some file formats play well only on a certain engine, this media player was made with 3 engines, so that the user can select the required engine required for playing a particular file type. It also has an engine auto select mode, in which the player automatically selects the best engine for the particular type of file being played.

If your music collections is on a remote server (very handy to control you music from everywhere in the house) then Music Player Daemon (mpd) is a go to, full documentation and list of client there:
mpd

A nice and interesting media player: Gmusicbrowser. Its web describes it as:

An open-source jukebox for large collections of mp3/ogg/flac/mpc/ape files, written in perl.

It has a nice GUI. The default view shows the artists and bands from your collection and for the selected item it shows the list of albums including a thumbnail of the coverart (if available). It also offers themes so that it looks like Exaile, QuodLibet or Rhythmbox.

Gnome Media Player is new and doesn't come with too many features but for just playing movies, its great. It supports the VLC, Xine and Gstreamer engines for playing media. It also has the ability to switch between the engines, and an engine auto select mode which automatically selects the best engine for playing a particular type of file.

It's in the Ubuntu 10.10 official repositories so you can search for it in the Ubuntu Software Center.

SMPlayer is recommended as it has a really good interface and uses the superb MPlayer as its backend.
It supports a great variety of codecs, and plays practically any major format you throw at it. It uses Qt, and integrates reasonably well with an Ubuntu desktop.

You can install SMPlayer by either searching via Software Center or by running Terminal and passing the command: sudo apt-get install smplayer

I recommend installing SMplayer instead of VLC. SMPlayer supports VDPAU. (I heard that VLC also supports VDPAU, but I have not been able to find any PPAs with a VLC package that supports VDPAU / VAAPI without errors.)

Glossary:

VDPAU: The VDPAU API allows video programs to offload portions of the video decoding process and video post-processing to the GPU video hardware.